EP1882163A1

EP1882163A1 - Magnetoinductive flow meter and measuring tube for such a flow meter

Info

Publication number: EP1882163A1
Application number: EP06755005A
Authority: EP
Inventors: Thomas Zingg; Simon Stingelin
Original assignee: Endress and Hauser Flowtec AG; Flowtec AG
Current assignee: Endress and Hauser Flowtec AG
Priority date: 2005-05-16
Filing date: 2006-05-04
Publication date: 2008-01-30
Also published as: CN101194147A; WO2006122878A1; CN101194147B; RU2007146763A; RU2401990C2

Abstract

The invention provides that a measuring tube (2) for a magnetoinductive flow meter is produced at least proportionately from a magnetically conductive material whose relative permeability, µr, is substantially greater than one. The measuring tube at least proportionately consists of a ferromagnetic metal.

Description

description

Electromagnetic flowmeter and measuring tube for such a flowmeter

The invention relates to a measuring tube for a magnetic-inductive flow meter and a magnetic-inductive flow meter with such a measuring tube.

For measuring electrically conductive fluids flow meter are often used with a magnetic-inductive sensor. As is generally known, the flow rate of electrically conductive fluids, in particular liquids, can be measured with magnetic-inductive flow meters and can be mapped into corresponding measured values flowing in a pipeline. The measuring principle of electromagnetic flowmeters is known to be based on the fact that an electrical voltage that is induced due to charge separations in a traversed by a magnetic field partial volume of the flowing fluid, tapped by least two measuring electrodes and in a meter electronics of the flow meter to a corresponding measurement , for example, a volume flow measured value, is further processed. The person skilled in the art is equally familiar with the structure of the individual components as well as the mode of operation of electromagnetic flowmeters, for example also from DE-A 43 26 991, EP-A 1 460 394, EP-A 1 275 940, US Pat. EP-A 12 73 892, EP-A 1 273 891, EP-A 814 324, EP-A 770 855, US Pat

EP-A 521 169, US-B 67 63 729, US-B 66 58 720, US-B 66 34 238, US-B 65 95 069, US-A 60 31 740, the US-A 56 64 315, US-A 56 46 353, US-A 55 40 103, US-A 54 87 310, US-A 52 10496, US-A 47 04 908, US-A 44 10 926, US-A 2002/0117009 or WO-A 01/90702. To guide the fluid to be measured have sensors of the type described, as shown schematically in Fig., A inserted in the course of the fluid pipe used measuring tube to avoid short-circuiting the voltage induced in the fluid at least on his the fluid Contacting inside is formed substantially electrically non-conductive. For insertion of the measuring tube in the course of the fluid-carrying pipe end of the measuring tube in each case a corresponding flange or the like is provided. Industrially used sensors of the type described in this case usually each have a measuring tube, which by means of a metallic support tube and an applied on this inside, consisting of electrically insulating material layer - the so-called liner - is formed. The use of a measuring tube constructed in this way, among other things, ensures a mechanically very stable and robust construction of the measuring sensor and, to that extent, also of the flow meter as a whole. As a material for the liner, for example, hard rubber, polyfluoroethylene, polyurethane or other chemically and / or mechanically resistant plastics are used, while carrier tubes of the type described, in order to avoid impairment of the magnetic field, esp. A possible short-circuiting thereof via the measuring tube, conventionally are made of a non-ferromagnetic, especially paramagnetic, material, such as stainless steel or the like. By an appropriate design of the support tube thus an adaptation of the strength of the measuring tube to the mechanical stresses present in each case can be realized, while by means of the liner adjustment of the measuring tube to the applicable for the particular application chemical, esp. Hygienic, requirements can be realized. Usually, materials are used which each have a nominal, ie effective or average relative permeability μr, which is substantially less than 10, in particular less than 5. It is known that the relative permeability μ indicates how much the magnetic soot density (= magnetic induction) is increased in comparison to the magnetic soot density in air or vacuum whose permeability μo (induction constant) is equal to 1.256 • 10 ⁶ Vs-Am ¹ , when the material in question is introduced into selbiges magnetic field, ie it applies to the permeability μ of the material used, the relationship μ = μ. • μo.

The magnetic field required for the measurement is of a corresponding

Magnetic system generates, which contains a coil assembly with mostly two field coils, corresponding coil cores and / or pole pieces for the field coils and possibly the coil cores outside the measuring tube connecting magnetic-conductive guide plates. However, magnetic field systems with a single field coil are also known. The magnetic field system is usually, as also indicated in Fig. 1, arranged directly measuring tube and supported by this.

To generate the magnetic field, an excitation current I supplied by a corresponding measuring device electronics is allowed to flow in the coil arrangement. This is usually a clocked bi-polar rectangular AC in modern sensors. In US-B 67 63 729, US-A 60 31 740, US-A 44 10 926 or EP-A 1 460 394 are examples of the generation of such exciter current serving circuit arrangements and corresponding switching and / or control methods described for it. Such a circuit arrangement usually comprises a power supply driving the coil current and a bridge circuit designed as an H or T circuit for the modulation of the exciter current.

The voltage generated in Ruid according to Faraday's law of induction becomes between at least two galvanic, that is wetted by the liquid, or tapped between at least two capacitive, ie, for example, arranged within the tube wall of the measuring tube, measuring electrodes as a measuring voltage. In the most common case, the measuring electrodes are arranged diametrically opposite one another so that their common diameter is perpendicular to the direction of the magnetic field and thus perpendicular to the diameter on which the coil arrangements lie; however, the measuring electrodes may also be arranged on the measuring tube in a non-diametrically opposite manner, cf. esp. the

US-A 56 46 353. The tapped by means of the measuring electrodes measuring voltage is amplified and processed by means of an evaluation circuit to a measurement signal that can be registered, displayed or in turn further processed. Corresponding measuring electronics are likewise known to the person skilled in the art, for example from EP-A 814 324, EP-A 521 169 or WO-A 01/90702.

As already indicated, comes in sensors of the type described the leadership of the magnetic field inside and outside of the measuring tube of particular importance. Commonly used measures for influencing the magnetic field are in addition to the use of non-ferromagnetic measuring tubes, for example, as u.a. also in the

Described US-B 65 95 069, given by the use of suitably shaped and as close to the fluid arranged pole pieces for the field coils and / or the use of magnetically conductive, esp. Ferromagnetic, materials for the return of the magnetic field outside of the measuring tube ,

A significant disadvantage of such sensor with metallic support tube is to watch that on the one hand considerable technical effort is required to form the magnetic field in sufficient for the required measurement accuracy measures and lead. On the other hand, the concomitant use of relatively expensive non-ferromagnetic metals for the support tubes, such as e.g. Another disadvantage of conventional magnetic field systems is also to be seen in the fact that the magnetic field, as shown schematically in FIG. 1, is formed very inhomogeneous within the measuring tube lumen and thus the measuring voltage can to a considerable extent also be dependent on the flow profile of the fluid in the measuring tube.

An object of the invention is therefore to improve magnetic-inductive sensor to the effect that on the one hand cost-effective manufacture of the same can be done and that on the other hand, the expression of the magnetic field required for the measurement can be optimized in a simple and inexpensive, yet very efficient way can. To achieve this object, the invention consists in a serving an electrically conductive fluid measuring tube of a magnetic-inductive flow meter, and wherein the measuring tube at least partially, esp. Mostly, consists of a magnetically conductive material having a relative permeability, μ which is substantially greater than one, in particular greater than 10.

Furthermore, the invention consists in a magnetic-inductive flow meter for a fluid flowing in a conduit, comprising such a measuring tube.

According to a first embodiment of the measuring tube of the invention, the metallic components of the measuring tube and / or the entire measuring tube consist predominantly of magnetically conductive material.

According to a second embodiment of the measuring tube of the invention, the magnetically conductive material has a relative permeability, μ, which is substantially greater than 10, in particular greater than 20, is.

[0022] In a third embodiment of the measuring tube of the invention, the magnetically conductive material has a relative permeability μ _"which is less than 1000, esp. Less than 400, is.

According to a fourth embodiment of the measuring tube of the invention, the magnetically conductive material has a relative permeability, μ, which is in a range between 20 and 400.

According to a fifth embodiment of the measuring tube of the invention, at least one central tube segment of the measuring tube, esp. Along a self-contained circumference of the measuring tube, made of the magnetically conductive material.

According to a sixth embodiment of the measuring tube of the invention, the magnetically conductive material is distributed over an entire length of the measuring tube and / or over an entire circumference of the measuring tube, in particular uniformly.

According to a seventh embodiment of the measuring tube of the invention, the measuring tube consists at least proportionally of ferromagnetic metal.

According to an eighth embodiment of the measuring tube of the invention, the measuring tube is at least partially made of soft magnetic metal.

According to a ninth embodiment of the measuring tube of the invention, the measuring tube consists at least partially of hard magnetic metal.

According to a tenth embodiment of the measuring tube of the invention, the magnetically conductive material has a layer thickness which is much smaller than an inner diameter of the measuring tube.

[0030] According to an eleventh embodiment of the measuring tube of the invention, the inner

Diameter of the measuring tube and the layer thickness of the magnetically conductive material so dimensioned that a ratio of layer thickness of the magnetically conductive material to inner diameter of the measuring tube is less than 0.2, esp. Less than 0.1. According to a twelfth embodiment of the measuring tube of the invention, the measuring tube is at least on its fluid-contacting inside substantially electrically non-conductive.

According to a thirteenth embodiment of the measuring tube of the invention, the measuring tube is formed by means of a serving as the outer tube wall and / or as an outer sheath, esp. Metallic and / or electrically conductive carrier tube, which lined inside with at least one layer of electrically insulating material is. According to a development of this embodiment of the invention, the support tube has a wall thickness which is much smaller than an inner diameter of the support tube. In particular, the inner diameter and the wall thickness of the support tube are dimensioned such that a ratio of the wall thickness of the support tube to its inner diameter is less than 0.5, esp. Less than 0.2, is. According to another development of this embodiment of the invention, such a magnetically conductive material is used that the ratio of the wall thickness of the support tube to its inner diameter multiplied by the relative permeability, ^, of the magnetically conductive material gives a value which is less than 5, esp. Less than 3, is and / or is greater than one, in particular greater than 1.2, is. Another aspect of this embodiment of the invention is that the carrier tube is at least partially, in particular predominantly or continuously, made of the magnetically conductive material.

According to a first embodiment of the flowmeter of the invention, this further comprises a measuring and operating circuit, fed by the measuring and operating circuit magnetic field system, at least temporarily by means of at least one of the measuring tube or in the vicinity arranged field coil a lumen of Measuring tube passing through, in particular clocked, magnetic field generated, and at least two measuring electrodes for picking up electrical potentials and / or electrical voltages, which are induced in flowing through the measuring tube and penetrated by the magnetic field fluid. In order to generate measured values which represent at least one parameter describing the fluid to be measured, the measuring and operating circuit is furthermore connected at least temporarily to at least one of the measuring electrodes. According to a development of this embodiment of the invention, the measuring electrodes are spaced apart from the at least one field coil on the measuring tube and / or within its tube wall. In particular, the at least two measuring electrodes are arranged on the measuring tube in such a way that an electrode axis which connects them imaginarily intersects the magnetic field passing through the lumen of the measuring tube, at least at times, substantially perpendicularly. Furthermore, the magnetically conductive material is at least in the region of a central tube segment of the measuring tube, in particular along a closed perimeter of the measuring tube, so distributed and the at least one field coil and the measuring electrodes are arranged on the measuring tube, that the at least temporarily generated during operation magnetic field both in the field coil and in the region of the measuring electrodes, esp. With substantially the same direction and / or substantially the same magnetic Russdichte , is coupled into the lumen of the measuring tube. In addition, the magnetically conductive material is distributed at least in the region of a central tube segment of the measuring tube, in particular along a closed circumference of the measuring tube, and the at least one field coil and the measuring electrodes are arranged on the measuring tube in such a way that the magnetic field generated at least intermittently the lumen of the measuring tube is formed at least in the region of the central tube segment such that it is oriented at least predominantly perpendicular to the imaginary electrode axis, at least in the region of the tube wall even at a perpendicular distance from the imaginary electrode axis of more than a quarter of an inner diameter of the measuring tube.

According to a second embodiment of the flowmeter of the invention, this further comprises at least one outside the measuring tube extending magnetic feedback for guiding the magnetic field outside the measuring tube. According to a development of this embodiment of the invention is a, esp. Measured in the range of the measuring electrodes, mean distance between the magnetic return and the measuring tube chosen so that a distance-diameter ratio of the average distance to an outer diameter of the support tube is smaller than one, in particular less than 0.5, is. Furthermore, in this embodiment of the invention, it may be advantageous to use such a magnetically conductive material that the ratio of the mean distance to the outer diameter of the support tube multiplied by the relative permeability, μ _r , of the magnetically conductive material gives a value that less than 100, esp. Less than 60, is.

A basic idea of the invention is to improve the efficiency of the

Magnetic field system to be achieved in that magnetic-inductive sensors, instead of the usually used for magnetic or only to a small extent conductive measuring tubes (^ ^ 1), equipped with magnetically highly conductive material measuring tubes (^ »1).

The invention is also based on the surprising finding that the use of magnetically highly conductive material for the measuring tube within the Meßrohrlumens at least in the vicinity of the measuring electrodes both a significant gain and a considerable homogenization and extent a homogenization of the magnetic field can be effected ,

An advantage of the invention is that this improvement of the magnetic field system can be achieved even by means of measuring tubes of the type described, which in Compared to conventional sensors are much cheaper to manufacture.

Details of the invention and advantageous embodiments will now be explained in more detail with reference to embodiments illustrated in the figures of the drawing for a magnetic-inductive flow meter and with reference to experimentally determined for different configurations of the sensor according to the invention magnetic field data:

Fig. 1 shows the propagation of the magnetic field in a conventional magnetic inductive sensor,

Fig. 2 shows schematically partly in a cross section and partly in the form of a block diagram an electromagnetic flowmeter with a measuring tube,

FIG. 3 shows the propagation of the magnetic field within a cross-section of a magnetic inductive sensor according to the invention spanned by an electrode axis and a field coil axis, FIG.

Fig. 4a, b, c shows within the cross section of Fig. 3 for various magnetic-inductive sensor detected L2 standards of the magnetic Russdichte B and of their acting in the direction of the electrode axis or in the direction of the field coil axis components in each case depending on a relative permeability of the measuring tube material,

FIG. 5 shows, within the cross section of FIG. 3, curves of the magnetic Russet density B along the respective electrode axis as a function of a distance from the center of the electrode axis, for various magnetically inductive sensors.

FIG. 7 shows, within the cross-section of FIG. 3, total deviations of the amount of soot density, determined for various magnetic-inductive sensors, from the mean value of the soot density B measured there as a function of a relative permeability of the measuring tube material, FIG.

Fig. 8, 9 show for various magnetic-inductive sensor according to FIG. 2 or 3 determined dependencies of optimum relative permeability for the measuring tube material as a function of different geometrical design variables for the sensor, and

Fig. 10,11 show for various magnetic-inductive sensor

12a, b, c shown in FIGS. 2 or 3 determined dependencies of

13a, b, c magnetic field within the cross section of Fig. 3 on the basis of the magnetic field self-characterizing measured variables as a function of the relative permeability of the measuring tube material and various geometric design variables for the sensor. In Fig. 2 and 3, a flow meter is shown schematically, with the at least one physical measurement of an electrically conductive and flowing fluid 11, for example, a volumetric flow, is to be determined. The flowmeter comprises a magnetic-inductive sensor 1 and a measuring and operating circuit 8 coupled thereto for driving the same and for generating, in particular digital, measured values which represent at least one parameter describing the fluid. In order to pass on calculated measured values, the measuring and operating circuit 8 implemented, for example, also using a microcomputer 10, can also communicate with a higher-level process control computer 9 via a corresponding data transmission system 16.

To the sensor 1 includes a in the course of the fluid 11 leading - but not shown here - tube inserted measuring tube 2 with a pipe wall surrounded, at least temporarily flowed through by the measured fluid 11 Meßrohrlumen. For connecting the measuring tube 2 to the pipeline, corresponding connecting elements, e.g. Flanges, provided.

During operation of the flow meter, at least part of the measuring tube lumen is at least temporarily interspersed by a magnetic field. The magnetic field, which is kept substantially constant at least intermittently, in particular also cyclically, runs at least in sections perpendicular to a longitudinal axis z of the measuring tube coinciding with the flow direction of the fluid 11, whereby in the fluid one with the at least one measured variable of the fluid, for example the flow velocity and / or the volume flow, corresponding measurement voltage U is induced. On its fluid contacting inside the measuring tube is substantially electrically non-conductive, so that a short-circuiting of the induced by the magnetic field measuring voltage U across the measuring tube 2 is avoided.

To generate this required for the measurement of the at least one parameter magnetic field with a sufficiently high soot density B, the sensor 1 further comprises a powered by the measuring and operating circuit 10 magnetic field system by at least one of the measuring tube 2 or in the vicinity of which arranged field coil generates a, at least temporarily, a lumen of the measuring tube 2 passing through, esp. Clocked, magnetic field. In the exemplary embodiment shown here, the magnetic field system comprises first field coil 6 and a second field coil 7, in particular electrically connected in series or parallel to the first field coil 6. The field coils 6, 7 are arranged opposite one another on the measuring tube 2, specifically in accordance with FIG advantageous embodiment of the invention so that the two field coils virtually connecting coil axis y coincides with a diameter of the measuring tube 2, which is substantially perpendicular to the longitudinal axis z of the measuring tube. 2 runs. The tube wall and the measuring tube lumen with the fluid 11 passing through the magnetic field now arises when a corresponding exciting current is allowed to flow in the field coils 6, 7, for example a pulsed DC or AC current. Each of the field coils 6, 7, as usual in such magnetic field systems, be wound around a magnetically conductive core, which in turn can cooperate with a corresponding pole shoes, cf. eg the

US-A 55 40 103; However, the field coils can also, as shown schematically in FIG. 1, be coreless air-core coils. In order to improve the magnetic properties of the magnetic field system, it is further possible to provide a magnetic return 17 which is laid outside the measuring tube 2 and serves to guide the magnetic field outside the measuring tube within the smallest possible volume. For example, the field coils 6, 7, as is also customary in the case of such measuring sensors, can be magnetically coupled to one another by means of such magnetic feedbacks 17 laid outside the measuring tube. The magnetic field system is further advantageously designed in such a way, esp. The two field coils 6, 7 are dimensioned and aligned with each other so that the magnetic field generated within the measuring tube 2 at least with respect to the coil axis y largely symmetrical, esp. At least C ₂ - rotationally symmetrical (C ₂ symmetry = 180 ° rotation Sysmetrie) is formed.

For picking up electrical potentials and / or electrical voltages which are induced in the fluid flowing through the measuring tube 2 and interspersed by the magnetic field, the sensor further comprises at least two measuring electrodes, at least temporarily in the operation of the flow meter with the measuring and Operating circuit 8 are connected, wherein a arranged on an inner side of the tube wall of the measuring tube 2 first measuring electrode 4 the tapping of a dependent of the at least one measured variable first potential and a measuring tube equally arranged second measuring electrode 5 tapping a likewise dependent on the at least one measured second Serve potentials. The measuring electrodes 4, 5 are arranged at a distance from the at least one field coil on the measuring tube and / or within the tube wall and that according to an advantageous embodiment of the invention so that the two measuring electrodes 4, 5 imaginary connecting electrode axis x substantially perpendicular to the coil axis y and / or the measuring tube longitudinal axis z runs. Under the influence of the magnetic field B free charge carriers located in the flowing fluid migrate depending on the polarity in the direction of one or the other measuring electrode 4, 5 from. The measuring voltage U built up between the measuring electrodes 4, 5 is substantially proportional to the flow velocity of the fluid averaged over the cross section A of the measuring tube 2 shown in FIG. 1 and thus also a measure of its volume flow. In the embodiment shown here, the measuring electrodes 4, 5 are practically on a second diameter of the measuring tube 2, which is both substantially perpendicular to the Meßrohrlängsachse z and substantially perpendicular to the coil axis y. The measuring electrodes 4, 5 may be formed, for example, as shown schematically in FIG. 1, as galvanic, that is, the liquid contacting electrodes. Alternatively or in addition thereto, however, capacitive electrodes, for example electrodes arranged within the tube wall of the measuring tube 2, may also be used as measuring electrodes 4, 5. Moreover, it is advantageous if the magnetic field system is designed such that the magnetic field also has at least one cvSymmtrie with respect to the electrode axis x. According to one embodiment of the invention, the magnetic field is also designed so that it is substantially symmetrical within the Meßrohrlumens at least temporarily with respect to the aforementioned imaginary reference axes x, y, z in such a way that it substantially each at least one c2 symmetry (= 180 ° rotational symmetry).

The measuring electrodes 4, 5 as well as the at least one field coil 6 and the

Field coils 6, 7 are finally electrically connected via corresponding connecting lines 4, 5, 6, 7 with the measuring and operating circuit 8 controlling the operation of the flowmeter.

According to the invention it is further provided that measuring tube at least partially, in particular predominantly, to produce from a magnetically conductive material having a relative permeability μ _r , which is substantially greater than one. According to one embodiment of the invention, that region of the measuring tube also consists of the magnetically conductive material in which the measuring electrodes are held.

Surprisingly, investigations have shown that using magnetic, esp. High, conductive material for the measuring tube 2 at least in the region of a central, cut by the imaginary field coil axis y and the imaginary electrode axis x cut tube segment of the measuring tube 2 significant improvements, at least stationary, so for the measurement of the at least one parameter held sufficiently constant magnetic field in the measuring tube lumen can be achieved, especially in terms of its flux density B and / or its distribution and orientation in the measuring tube lumen. Thus, for example, for a cross-section of the measuring tube 2 spanned by the field coil axis y and the electrode axis x and substantially corresponding to the cross-section A shown in FIG. 2, it could be ascertained that the flux density B of at least the stationary magnetic field at a relative permeability μr of greater than 10 is more surprising Way can assume disproportionately high values. This can be easily verified for concrete measuring tubes and magnetic field systems, inter alia, based on the so-called L ² standard of the soot density B. The L ² -Norm IIBII _{L2 of} the soot density B practically indicates how much magnetic field is contained in this cross-section A of the measuring tube or how high the magnetic energy of the magnetic field is, and can be calculated based on the formula [0059]

B, - | W ^ B B, dxd \

(1)

[0060] are calculated. A possible course of the L ² -norm IIBII _{L2 of} the soot density B as a function of the selected relative permeability μ _^ is shown by way of example in FIG. 4a. In addition to this improvement in the magnetic field in the entire measuring tube lumen, which is based on the use of magnetically highly conductive material, a considerable increase can also be ascertained, at least in the amount IBI of the soot density B, in the region of the abovementioned tube segment, in particular within the abovementioned cross section A of FIG Measuring tube or, as exemplified in Fig. 5, at least along the electrode axis x and in their immediate vicinity. As a result of this increase in the soot density B, an equally significant increase in the measuring voltage U can be observed in comparison to conventional magneto-inductive flow sensors with a similar structure.

Furthermore, it has been found that, depending on the actual dimensioning of the measuring tube and the magnetic field system including any feedback for the measuring tube an optimal relative permeability μ can be found in the case of stationary magnetic field, the soot density B and thus also their L ² -Normal IBII _{L2 is} maximum, cf. See also Fig. 4a. In a corresponding manner, the sensor has a maximum sensitivity, in which the flowing, penetrated by the magnetic field Ruid causes a maximum measuring voltage U between the two measuring electrodes. Further investigation led to the realization that the optimum relative permeability μ _^, depending on the dimensions of the sensor approximately in the range between 10 and 1000, esp. In the range between 20 and 400, is located.

It has also been found that by using magnetically conductive material for the measuring tube, the stationary magnetic field can be improved not only in terms of soot density B, but also in that it is the same in field coil axis y direction compared to conventional sensors Design, at least within the aforementioned cross-section A, experiences a much more uniform and straighter alignment, symbolized by the in Fig. 3. Within the Meßrohrlumens almost parallel field lines. This Among other things, it manifests itself in the fact that the magnetic field is coupled into the measuring tube lumen, at least within the mentioned cross-section A, both in the area of the field coils and in the region of the measuring electrodes, in particular with essentially the same direction and / or essentially the same magnetic soot density B. , In other words, bypasses of the magnetic field past the flow region relevant to the measurement can be avoided or at least very effectively minimized.

In particular, it has been found that by suitable choice and distribution of the magnetically highly conductive material, tailored to the actual selected for the measuring tube nominal diameter and / or wall thickness, at least in the region of the central tube segment of the measuring tube, esp. Within the aforementioned cross section A, at least acting in the direction of the coil axis y shares B _{y of} the magnetic field can be increased, while at the same time a reduction in the direction of the electrode axis x acting portions B _{x of} the magnetic field can be achieved.

The aforementioned effects can in turn be very clearly verified by the respective L ² standard HB _X II _L2 and IIB _y II _{L2 of} the individual components B _x and B _{y of} the soot density B, expressed mathematically by:

[0065]

(2)

[0066]

, (3)

Possible courses of the L ² -Norm IIB _y ll _L2 of actually required for measuring at least the volume flow magnetic field components B _y and the L ² - IIB _X II _L2 standard, for example, for the measurement of volume flow rather unwanted magnetic field components B _x are in each case depending on the selected relative permeability μ _r in FIGS. 4b and 4c shown by way of example. Clearly visible are the initially positive and very steep, finally opening into a maximum value increase in the direction of the coil axis acting magnetic field components B _y at the same time very steeply sloping course of acting in the direction of the electrode axis magnetic field components B _x .

In addition, the magnetic field can be improved by the use of magnetically highly conductive material for the measuring tube also in terms of its homogeneity to a considerable extent. This shows, for example, that a Deviation of the amount IBI of the soot density B within the measuring tube lumen, but at least within the cross section A, from the mean measured there

B of the soot density B, so practically a variance of the amount IBI of the soot density B, the smaller, the greater the relative permeability μ _{^ has} been chosen for the magnetically conductive material and so far for the measuring tube itself. The mean

B of the soot density B as well as a corresponding total deviation s can be easily determined for the cross-section A, for example based on the following mathematical relationships: [0069]

(4) [0070]

B = - flB dx dy

^A A

, (5)

Wherein the total deviation s at least qualitatively may have the dependency on the relative permeability μr shown by way of example in FIG. 6.

Very clearly, this homogenization and, to that extent, the homogenization of the magnetic field based on a relative deviation

the soot density B in cross-section A from their local mean

B, where is the relative deviation? can be calculated from the following mathematical relationship: [0073]

, (6)

In particular, can be achieved by a suitable distribution of the magnetically conductive material via the measuring tube readily that the stationary magnetic field is designed such that the instantaneous total deviation s of the averaged over the cross section A Russdichte B of the current average B of the Russdichte B in selbigem cross-section A or their variance is less than 0.005 and / or that the corresponding relative deviation

the soot density B from the mean

B is less than 1%, especially less than 20% e, in cross-section A. In addition, by using the magnetically highly conductive material for the measuring tube, the magnetic field can be formed such that it also intersects perpendicular to the imaginary electrode axis x parallel secant of the cross-section A perpendicular, of the imaginary electrode axis x a quarter-length of an inner diameter of Measuring tube D is spaced.

As a result, the above-described rectification of the magnetic field and / or

Comparing the amount IBI of the Russdichte, so far as the homogenization of the magnetic field, u.a. also to the fact that the measuring voltage U compared to conventional magnetic-inductive sensors with similar structure less sensitive to any disturbances of the Ruidströmung, for example by entrained foreign matter, bubbled gases and / or changes in the flow profile, reacts and is so far very robust. Likewise, an improvement in the magnetic field characteristics relevant for the measurement of the at least one physical measured variable, in particular an increase in the soot density B in the region of the electrodes 4, 5 and the electrode axis x as well as within the central tube segment, can be achieved. As a result, the magnetic field system has a higher efficiency and the measurement values corresponding to the measurement voltage U, for example the flow velocity and / or the volume flow, can be determined more precisely.

According to one embodiment of the invention, the magnetically conductive material is distributed at least over a region of a central tube segment of the measuring tube 2, in which the electrodes and the at least one field coil are arranged. Alternatively or additionally, the magnetically conductive material according to a further embodiment of the invention at least along a closed perimeter of the measuring tube 2 and / or over an entire length of the measuring tube 2, esb. Evenly distributed. Furthermore, the magnetically conductive material may also be distributed over the entire measuring tube 2, be it largely homogeneous or substantially heterogeneous.

According to a further embodiment of the invention is provided, the magnetically conductive material as a substantially continuous layer in the measuring tube to apply. In this case, the magnetically conductive material preferably has a layer thickness d which is much smaller than an inner diameter D of the measuring tube. Alternatively or in addition, the inner diameter D of the measuring tube 2 and the layer thickness d of the magnetically conductive material are dimensioned such that a ratio of the layer thickness of the magnetically conductive material to the inner diameter D of the measuring tube is less than 0.2, in particular less than 0.1, is.

In order to avoid increased eddy current and / or increased re-magnetization losses in the measuring tube 2, the latter can also be constructed in layers of a plurality of such alternately, especially coaxially, superimposed layers of magnetically conductive material and electrically nonmagnetic material , According to one development of the invention, therefore, at least one layer, in particular but a plurality of layers spaced apart radially from one another, of the magnetically conductive material is an electrically substantially non-conductive material and / or at least one layer, but in particular a plurality of layers spaced radially apart from one another to embed electrically substantially non-conductive material in magnetically conductive material. In addition, in connection with the sensor according to the invention, if necessary, but also further measures to minimize eddy currents can be applied, for example, in EP-A 1 460 394 and / or US-A 60 31 740 proposed method for controlling the Magnetic field system driving excitation current.

In the embodiment shown here, the measuring tube 2, as quite customary with sensors of the type described, by means of a serving as an outer tube wall and / or as an outer sheath, esp. Metallic and / or magnetically conductive, carrier tube 21 formed inside with at least one layer 22 of electrically insulating material, such as Ceramics, hard rubber, polyfluoroethylene, polyurethane or the like, the so-called liner, lined; in the case of measuring tubes made entirely of a comparatively non-conductive plastic or of a ceramic, in particular of alumina ceramic, such an additional electrically non-conductive layer is by contrast not absolutely necessary. According to one embodiment of the invention, the support tube consists at least partially of the magnetically conductive material, in particular a magnetically conductive metal.

The support tube 21 has, as shown schematically in FIGS. 2 and 3, a wall thickness d _τ , which is much smaller at least compared to the inner diameter D _{x of} the support tube. According to a further embodiment of the invention it is further provided that the inner diameter D _x and the wall thickness d of the support tube are dimensioned such that a diameter-wall thickness ratio w = d _τ / DT of the wall thickness d _{τ of} the support tube to the inner Diameter D _x less than 0.5, esp. Less than 0.2, is. According to a further embodiment of the invention, such a magnetically conductive material is used for the support tube 21 and its wall thickness d _τ and inner diameter D _x are dimensioned so that the aforementioned diameter to wall thickness ratio w multiplied by the relative permeability μ, the magnetic conductive material gives a value d _τ / D _τ • μ _r , which is less than 5, esp. Less than 3, is. Alternatively or in addition, such a magnetically conductive material is used for the support tube and its wall thickness d _τ and inner diameter D _x are dimensioned such that this by means of the diameter-wall thickness ratio w and the relative permeability μ, the magnetically conductive Material formed wall thickness form factor d _τ / D _τ • μ _r for the support tube and as far as the entire measuring tube assumes a value that is greater than one, esp. Greater than 1.2, is. Further studies have also shown that in addition to the wall thickness d _τ and the inner diameter D _{x of} the magnetically conductive support tube and the geometry and / or the spatial arrangement of the magnetic field outside the measuring tube serving magnetic return 17 considerable influence on the course of Magnetic field within Meßrohrlumen, esp. But on the spatial distribution of the Russdichte B and / or their amount within the cross-section A and / or Meßrohrlumens take. In particular, it was found that, for example, for a support tube in which the wall thickness d _τ , the inner diameter D _x and the relative relative permeability μ, are given in the sense of uniformly distributed over the cross-section A Russdichte B at least in Area of the measuring electrodes an optimal average distance h ,. between the magnetic return 17 and the support tube can be determined. Conversely, in the case where wall thickness d _τ , inner diameter D _x and lateral installation dimensions for the sensor are predetermined or limited, an optimum permeability μ _r which is as uniform as possible for the magnitude of the magnetic field can be determined. According to another embodiment, therefore, the support ear and the return is further designed and dimensioned so that a distance-diameter ratio w _r = h / (d _x + D _x ) of the average distance h _r to an outer diameter (d _x + D _x ) of the support tube is less than one, esp. Less than 0.5, is. According to a further embodiment of the invention, such a magnetically conductive material is used for the support tube and its wall thickness d _x and inner diameter D _x are dimensioned such that the aforementioned distance to diameter ratio w _r multiplied by the relative permeability μr of the magnetically conductive Material gives a value μr • h, / (d _x + D _x ), which is smaller than 100, esp. Less than 60, is. Alternatively or in addition, it is further provided to use such a magnetically conductive material for the support tube and its wall thickness d _τ and inner diameter D _x to be dimensioned so that this formed by the distance-diameter ratio w _r and the relative permeability μ _{r of} the magnetically conductive material feedback form factor U ₁ • h / (d _x + D _x ) assumes a value for the support tube and so far for the entire measuring tube, which is greater than one.

The optimum for a specific configuration of the measuring tube and the magnetic field system in terms of a maximum measuring voltage U relative permeability μ, used for the measuring tube magnetically conductive material can for practically relevant diameter to wall thickness ratio w and / or practically relevant distance Diameter ratio w _r can be read directly from the empirically determined characteristic curves shown in FIGS. 7 and 8.

Although, as previously shown by the example of the feedback form factor μ _r • h / (d _x + D _x ), also the dimensioning of the feedback quite the propagation of the magnetic field, esp. The distribution of the soot density B within the cross-section A. , Surprisingly, it could be found that the inner diameter and the wall thickness of the support tube or more generally the inner diameter D of the measuring tube and the distribution, esp. The layer thickness of the magnetically conductive material in the measuring tube in this respect a much greater influence can take on the propagation of the magnetic field within the Meßrohrlumens and extent to the extent and the robustness of the measurement voltage U. Thus, in FIG. 9, curves for the above total deviation s from the mean value are shown

B and in Fig. 10 for the relative deviation

from the mean

B, which were determined empirically for different diameter-wall thickness ratios w and different distance-diameter ratios w _r in the region of the cross-section A. In this case, FIGS. 9 and 10 for each of the diameter-wall thickness ratios w (0.0005 .... 0.1876) selected here, in each case the same four different distance-diameter ratios w _r (0.25; 05; 0.75; 1 ) and in the manner defined by the respective diameter - wall thickness ratio w and by the uniformly selected line style (w = 0.0175 -; w =

0.0629: -; w = 0.1253: -; w = 0.1876:; w = 0.25: -)

Ensemble has been summarized. It can be clearly seen that for practically relevant diameter-wall thickness ratios w of greater than 0.01 on the one hand sufficiently large relative permeability μ, of greater than or equal to 10 barely an influence of the feedback on the relative deviation? and insofar as the shape of the magnetic field within the cross-section A can be determined. On the other hand, for said Wandstärke- ratios w of greater than 0.01 at a sufficiently large chosen relative permeability μ _^ of greater than or equal to 10, only marginal improvements of the magnetic field in the sense of at least amount proper uniform distribution of the carbon black density B can be obtained within the cross section A.

In addition, it is apparent from FIGS. 1 Ia, b, c and 12a, b, c shown gradients of the means as well as the L ² norms, in each case depending on the aforementioned ratios w and a both for the soot density B and their individual components B _x and B _y numerically determined that by using magnetically highly conductive material for the measuring tube at least for relative permeabilities μ _^ in the range between 10 and 50 in addition to reducing the force acting in the direction of the electrode axis x portion of the magnetic field and an increase in the magnetic energy at least within Cross-section A and insofar as an increase in the efficiency of the magnetic field system can be achieved.

It should be mentioned at this point that can be used as a magnetically conductive material for the realization of the invention structural steel, cast iron or a, for example by dispersion, doped with magnetically conductive particles composite material and / or plastic; Of course, other, in the context of the invention, magnetically conductive materials can serve as a material for the measuring tube, for example, such materials as have been conventionally used for the coil cores and / or the magnetic feedback or are. According to one embodiment of the invention is accordingly provided that the measuring tube, esp. Also the aforementioned carrier tube, at least partially made of ferromagnetic metal. In this case, the measuring tube, esp. Also the aforementioned carrier tube, at least partially made of soft magnetic metal and / or at least partially made of hard magnetic metal.

As can be easily seen from the preceding explanations, the sensor according to the invention is characterized by a variety of degrees of freedom that it the expert, esp. Even after a specification of external and / or internal installation dimensions (nominal diameter, installation length, side clearance etc.), by selecting a suitably suitable material for the measuring tube, an optimization of the magnetic field and thus, for example, an improvement in the sensitivity of the measuring voltage U to the measured from the Ruid To achieve parameters as well as their robustness against any disturbances in the fluid. With knowledge of the invention and against the background of the prior art mentioned at the outset, there is no difficulty for a person skilled in the art to determine the materials suitable for the particular application for the measuring tube.

Claims

claims

1. For guiding an electrically conductive fluid serving measuring tube (2) of a magnetic-inductive flow meter, wherein the measuring tube (2) at least partially, esp. Mostly, consists of a magnetically conductive material having a relative permeability, μ which is significantly greater than one, in particular greater than 10. 2. Measuring tube according to the preceding claim, wherein the magnetically conductive

Material has a relative permeability, μ, which is substantially greater than 10, in particular greater than 20, is. 3. Measuring tube according to one of the preceding claims, wherein the magnetically conductive material has a relative permeability, μ, which is smaller than 1000, esp. Less than 400, is. 4. Measuring tube according to one of the preceding claims, wherein the magnetically conductive material has a relative permeability, μ, which is in a range between 20 and 400. 5. Measuring tube according to one of the preceding claims, wherein at least one central tube segment of the measuring tube, esp. Along a self-contained

Circumference of the measuring tube, consists of the magnetically conductive material. 6. Measuring tube according to one of the preceding claims, wherein the magnetically conductive material is distributed over an entire length of the measuring tube and / or over an entire circumference of the measuring tube, esp. Evenly. 7. Measuring tube according to one of the preceding claims, wherein the measuring tube consists at least proportionally of ferromagnetic metal. 8. Measuring tube according to the preceding claim, wherein the measuring tube is at least partially made of soft magnetic metal. 9. Measuring tube according to claim 7 or 8, wherein the measuring tube consists at least partially of hard magnetic metal. 10. Measuring tube according to one of the preceding claims, wherein the magnetically conductive material has a layer thickness (d), which is much smaller than a

Inside diameter (D) of the measuring tube. 11. Measuring tube according to the preceding claim, wherein the inner diameter (D) of the measuring tube and the layer thickness (d) of the magnetically conductive material are dimensioned such that a ratio of layer thickness of the magnetically conductive

Material to inner diameter of the measuring tube is less than 0.2, esp. Less than 0.1, is. 12. Measuring tube according to one of the preceding claims, wherein the measuring tube (2) at least on its fluid contacting inside substantially electrically is formed non-conductive.

13. Measuring tube according to one of the preceding claims, wherein the measuring tube by means of serving as an outer tube wall and / or as an outer sheath, esp. Metallic and / or electrically conductive, support tube is formed, the inside with at least one layer of electrically insulating Material is lined.

14. Measuring tube according to the preceding claim, wherein the support tube at least partially, esp. Predominantly, consists of the magnetically conductive material.

15. Measuring tube according to the preceding claim, wherein the support tube predominantly, esp. Consistently, consists of metal.

16. Measuring tube according to one of claims 13 to 15, wherein the support tube a

Wall thickness (d _τ ), which is much smaller than an inner diameter (D _x ) of the support tube.

17. Measuring tube according to the preceding claim, wherein the inner diameter (D _x

) and the wall thickness (d _x ) of the support tube are dimensioned so that a ratio (d _x / D _x ) of the wall thickness (d _x ) of the support tube to its inner diameter (D _x ) is less than 0.5, esp. is.

18 measuring tube according to the preceding claim, wherein such a magnetically conductive material is used, that the ratio (d _x / D _x ) of the wall thickness (d _x ) of the support tube to its inner diameter (D _x ) multiplied by the Relative permeability (μ) of the magnetically conductive material results in a value (d _x / D _x • μ _r ), which is less than 5, esp. Less than 3, is.

19. A measuring tube according to claim 17 or 18, wherein such a magnetically conductive material is used, that the ratio (d _x / D _x ) of the wall thickness (d _x ) of the support tube to its inner diameter (D _x ) multiplied by the relative permeability (μ) of the magnetically conductive material gives a value (μ _r • d _x / D _x ) which is greater than one, in particular greater than 1.2.

20. Measuring tube according to one of the preceding claims, wherein the components consisting of metal consist predominantly of magnetically conductive material.

21. Electromagnetic flowmeter for a flowing in a conduit

Fluid comprising a measuring tube according to one of the preceding claims.

22. Electromagnetic flowmeter according to the preceding claim, further comprising: a measuring and operating circuit, -ein fed by the measuring and operating circuit magnetic field system, by means of at least one arranged on the measuring tube or in the vicinity of the field coil a, at least temporarily, a lumen of the measuring tube passing through, in particular clocked, magnetic field generated, and at least two measuring electrodes for tapping of electrical potentials and / or electrical voltages in the through the measuring tube wherein the measuring and operating circuit for generating measured values, which represent at least one parameter describing the fluid, is at least temporarily connected to at least one of the measuring electrodes.

23. Electromagnetic flowmeter according to the preceding claim, wherein the measuring electrodes of the at least one field coil spaced from the measuring tube and / or are arranged within the tube wall.

24. Electromagnetic flowmeter according to the preceding claim, wherein the magnetically conductive material at least in the region of a central tube segment of the measuring tube, esp., Along a self-contained circumference of the measuring tube, so distributed and the at least one field coil and the measuring electrodes so arranged on the measuring tube that the at least temporarily generated during operation magnetic field both in the field coil and in the region of the measuring electrodes, esp. With substantially the same direction and / or substantially the same magnetic Russdichte, is coupled into the lumen of the measuring tube.

25. Magnetic-inductive flow meter according to the preceding claim, wherein the at least two measuring electrodes are arranged on the measuring tube, that an imaginary this connecting electrode axis intersects at least temporarily passing through the lumen of the measuring tube magnetic field substantially perpendicularly.

26. Electromagnetic flowmeter according to the preceding claim, wherein the magnetically conductive material, at least in the region of a central tube segment of the measuring tube, esp., Along a self-contained circumference of the measuring tube, so distributed and the at least one field coil and the measuring electrodes so arranged on the measuring tube, that the at least temporarily generated magnetic field is formed within the lumen of the measuring tube at least in the region of the central tube segment such that it at least in the region of the tube wall at a vertical distance from the imaginary electrode axis of more than a quarter of an inner length Diameter (D) of the measuring tube is at least predominantly aligned perpendicular to the imaginary electrode axis.

27. Magnetic-inductive flowmeter according to one of claims 21 to

26, further comprising at least one outside the measuring tube extending magnetic feedback for guiding the magnetic field outside of the measuring tube.

28. Magnetic-inductive flowmeter according to the preceding claim, wherein a, esp. Measured in the region of the measuring electrodes, average distance (h _r ) between the magnetic return and the measuring tube is selected so that a distance-diameter ratio (h / (d _x + D _x )) of the average distance (h _r ) to an outer diameter (d _τ + D _x ) the support tube is less than one, esp. Less than 0.5, is. 29. A magneto-inductive flowmeter according to the preceding claim, wherein such a magnetically conductive material is used, that the ratio (h / (d _x + D _x )) of the average distance (h _r ) to the outer diameter (d _T + D _x ) of the support tube multiplied by the relative permeability (μ) of the magnetically conductive material gives a value (μ • h / (d _x + D _x )) which is less than 100, in particular less than 60.